The Physics of Backspin

In this video we perform an analysis of an object that rolls while slipping against the ground, like when a cue ball is hit with English in the game of pool. Surprisingly, the final velocity of the object is independent of the coefficient of friction, which means it will have the same final velocity whether sliding on a wooden table or on ice!
Special thanks to the Gingerbread Man in Carlisle, for giving us access to their pool room after hours. Thanks also to Jonathan Barrick, for making the disk, to my son Adam for helping record the pool scenes, and to Noah Lape for helping record the intro/outro clips.
Music for the pool scene:
That Science Ambient by ComaStudio, downloaded from pixabay.com/?u....
Background music for the rest of the video:
Music by Vincent Rubinetti
Download the music on Bandcamp:
vincerubinetti...
Stream the music on Spotify:
open.spotify.c...
Music for ending scene (attempts at sliding the wheel to a stop):
By REDproductions, downloaded from pixabay.com/mu....

[@AK56fire]

Awesome video there mate.. Great work.. Keep posting such incredible work and your channle will surely grow exponentially...

[@AllThingsPhysicsYouTube]

Thank you for the kind words. I hope you are right!

[@elti8614]

I feel like this is going to be the 3blue1brown for Physics. Great content, keep up with the good work!!

[@AllThingsPhysicsYouTube]

3b1b for physics...music to my ears! Please feel free to share with others who might be interested (and don't forget to subscribe!).

[@cheeseparis1]

Interesting videos that will show young people that physics is fun. And since you used the official universal fun constant as your number of tries, you get a new subscriber. Congrats!

[@AllThingsPhysicsYouTube]

Cool, thanks! And it was random that it ended up taking 69 tries, believe it or not.

[@noj5393]

Amazing video! The seemingly unintuitive relationship between sliding and backspin was made really clear by your video!

[@apoapzis]

At the time of commenting, this video has 304 views and the channel has 114 subscribers. Great video and stellar explanation, I'm sure this channel will grow exponentially in the years to come :D

[@AllThingsPhysicsYouTube]

Well, I hope you are right about exponential growth!

[@kevinlaws7259]

Very cool visualizations! I like the simulation of the real world below the real world.

[@eamonia]

You're so cool, dude. I'm really happy I found your channel and I just subscribed and will continue to like, share and comment on all your videos so more people will hopefully get a chance to enjoy and learn from your awesome content. Here's to ya, buddy. Keep up the great work.

[@AllThingsPhysicsYouTube]

Thanks so much for the kind words. I really appreciate the support!

[@onlyeyeno]

Thanks for another enjoyable, interesting and informative video. Best regards

[@mikip3242]

This vídeo is awesome. You have a gifted relaxed voice. The animations are essential for learning and you did the most fitting ones. You even have the right amount of humor. This is fantastic, really. I'm an astrophysicist by the way, and this is so nice and hypnotic to look at. Congratulations

[@AllThingsPhysicsYouTube]

Wow, thank you! If you're an astrophysicist be sure to watch the square orbit video, I think you'll like it. And if you haven't done so, please consider subscribing and share the videos with any colleagues you think might be interested.

[@mikip3242]

@@AllThingsPhysicsKZbin I certainly will. I admire teachers like you. There's not a lot of science education at this level on KZbin. There are good videos at the introductory level and also at the university level but having a bridge between the two is very needed and you are doing It nicely (Viascience does something similar but with less care on the visual part IMO). Also classical mechanics is much more fascinating that we normally think and It is nice to see It treated in a good way. Anyways, you earned a sub from Spain :)

[@AllThingsPhysicsYouTube]

@@mikip3242 For what it's worth, one of my long term goal is to produce several video series that will correspond to particular undergraduate physics courses (mechanics, math methods, etc.). But this will take many years.

[@alejandroguzman-ortega3449]

I just discovered this channel and wow... great presentation and explanations, keep it up!

[@photelegy]

15:13 He should have said "nice" except of "yes". Just saing 🤷🏻‍♂️

[@MathVisualProofs]

Excellent video and explanation. Very cool!

[@fisicamartin]

Great video, David! Congrats about your new channel, is great!!

[@Fine_Mouche]

1:43 why you don't show left and right impact on the ball ? i hope you will speak about at a moment of the video.

Awesome video!!! You explained very well the concepts and please keep going with your amazing work! This channel deserves a lot of subscribers!

[@AllThingsPhysicsYouTube]

Thank you so much!

[@jogadorjnc]

A very nice ending

[@AllThingsPhysicsYouTube]

Thanks!

[@angelorondini5835]

6:35 aren't positive and negative swapped there? (Because of the coordinate system)

[@AllThingsPhysicsYouTube]

No, I think everything is good. A positive rotational velocity has your thumb pointing into the screen so the point at the bottom of the wheel moves to the left.

[@angelorondini5835]

@@AllThingsPhysicsKZbin oh ok sorry you are right, it's already "backwards" (meaning that with x pointing right, y up and z exiting the screen positive rotation is counterclockwise, while here it's clockwise)

[@Loxodromius]

Great video, very well explained. Just one question: Can it happen that when the disc stops moving to the right it still keeps some rotational velocity? If so I believe it should acelarate to the left (instead of just going left with constant speed) untill all the rotational cinetic energy is converted into linear cinetic energy (at which point it kept with constant speed).

[@AllThingsPhysicsYouTube]

You are correct, and if you watch carefully this is exactly what happens in the video (both the real spinning disk and the simulation). In the particular example shown, the disc DOES stop translating to the right while it continues spinning, and so there is still a translational acceleration to the left. The friction force continues to act as long as the wheel is sliding against the table. This sliding motion continues until the rolling without slipping constraint is satisfied, and it is at that time when the friction force disappears and the disk rolls without slipping (and without any horizontal forces acting).

[@stuartl7761]

15:13 nice

[@mb59621]

A very cool video brother . I understood most of it , something i could not in college . Appreciate all the hardwork you put in . I still have a question. Can you explain why the wheel would undergo pure rolling after it reverses its direction? Why doesn't it undergo pure rolling when you gave it the backspin in the first place?

[@AllThingsPhysicsYouTube]

Same reason you can push a book against a table and make it slide. If you push very gently the book won’t move, but if you push harder you will overcome static friction and it will start to slide. With a wheel, throwing it with spin allows us to overcome static friction and do the wheel slides against the table. But, just like a book on the table, once sliding, kinetic friction acts to slow down the sliding until the object is no longer sliding. For a wheel that means the sliding slows down until it rolls without slipping. Does that make sense? Not sure I did a great job with the explanation.

[@mb59621]

@@AllThingsPhysicsKZbin Yes you did , thank you very much . Keep on doing the good work .

[@frasercrawford1]

Marvelous, this kind of straight forward, thoughtful approach to scientific analysis is always welcome. I'm amazed at how well put together the channel is given its age and size, I sense the algorithm will be picking up this gem soon enough. I don't know what sort of content you'll be doing in future, but a series of videos on classical and statistical thermodynamics would be nice (such as the ideal gas laws, entropy and multiplicity), it would be interesting to see how you would present it.

[@AllThingsPhysicsYouTube]

Thanks. I hope you're right about the algorithm!

[@sugarfrosted2005]

Rolling friction was the one part that my Newtonian mechanics course missed. Glad to finally catch up with that.

[@AllThingsPhysicsYouTube]

Glad I could help!

[@GaMeON159753456]

Nice video. Just curious, what software do you use to do the graphics and animations? I can’t think of a video editing software that supports equations.

[@AllThingsPhysicsYouTube]

Watch the square orbits videos. I mention the software in part 2. I use manim (mathematical animation engine).

[@anuragthakur4341]

I LOVED this video! Your manim skills are awesome

[@AllThingsPhysicsYouTube]

Thank you so much!! I'm still learning, but it's coming along.

[@yogoo0]

Nice

[@AllThingsPhysicsYouTube]

Thanks

[@harryepstein]

Nice. You might consider doing the hockey puck experiment where a spinning puck in motion stops spinning exactly at the same time when it comes to translational rest! The translational speed is related to the rotational speed..

[@marcoaltamura7512]

Without realizing I watched all your videos and love them. Would love to see a detailed analysis of a gyroscope, what forces and momenta act upon it and how it can "defy gravity" (this can make a good title/thumbnail/starting point).

[@AllThingsPhysicsYouTube]

A gyroscope is definitely on the list, but there are some others that are further along in the development process, so it might be a while.

[@marcoaltamura7512]

@@AllThingsPhysicsKZbin sure! This is actual quality content, keep going

[@zlac]

I never thought I would enjoy watching a hippie physicist explaining stuff on the internet!

[@AllThingsPhysicsYouTube]

Ha ha. Glad you enjoyed it!

[@roph82315]

Respect all the good content you have been making . I did these things a lot few time ago in high school . Never did physics after that but have always had a soft corner for this subject . Ignore the sily doubt if already read that 😅 , was a stupid calculation error .

[@sarahstover4485]

Great video!

[@HolyGrailOfGolf]

It's easier with a quarter. Hold the top edge with two fingers and slam your hand down on a table and the quarter shoots forward with a ton of backspin. If you're good at it it'll to 5 or 6 feet and come right back to you. It makes a lot of noise and dents the table ... it's a bar trick, really.

[@nick-dd3po]

Awesome video!

[@knopfir]

nice amount of tries at the end there

[@AllThingsPhysicsYouTube]

Heh...that was random believe it or not!

[@knopfir]

@@AllThingsPhysicsKZbin damn guess you can say thats a *NICE* coincidence there

[@danielbrowniel]

do you edit this with analog equipment?

[@AllThingsPhysicsYouTube]

Not sure I fully understand the question. If you're asking whether I used actual film, cutting the reels and splicing together, then no. But the scenes showing me throw the wheel with backspin uses an actual wheel. So I guess one could consider that "analog," in some sense.

[@Quadr44t]

2:50, totally unnecessary! But I like that you added that sound effect as well as that reaction 🤣 Edit: Hmmm, right so attempt 69 was the one 😶 hmmmmmmmmmmmmmmmmmmmmmmmmmm

[@AllThingsPhysicsYouTube]

Heh...I was a little worried about adding the sound effect. And yes, believe it or not, attempt 69 really was randomly the one!

[@Quadr44t]

@@AllThingsPhysicsKZbin Nah, I think those little things really add. Particularly because your videos are quite dense in information/theory. A small joke here and there helps people remain their focus. That said, I imagine it is real easily overdone, and can come across as cringy. Especially if it is a little forced. I think people can and do notice, as well as appreciate, authenticity in KZbinrs. I think here, the balance is fine! Haha, OK, nice coincidence then haha. (obviously the reason for "69"s significance being that it is the number you get when adding up all the possible devisors for integers 1 up to 9) Ok, maybe I stole that one directly from 3blue1brown.... just maybe....😶

[@AllThingsPhysicsYouTube]

@@Quadr44t Yes, trying to get a balance between "serious" and "relaxed" is not easy, and I suppose you will never satisfy everyone, but it's good to hear that at least one person thinks the balance is about right!

[@shanmu1091]

0:17 sail

[@coreC..]

Great video David. It reminds me of a game i developed decades ago (DOS era): pool/snooker/billiard. At that time i was searching for formulas and equations. I had to learn what was really going on, because i wanted the game to look/feel real. So i stumbled on this topic.. It's "only" physics!,.. you can calculate things according to laws,.. and you describe and demonstrate it well. But i do not like the brown color of the ground-plane in the video. That is all :-D try some more neutral color.. it doesn't distract so much.

[@AllThingsPhysicsYouTube]

Thank you. If the only thing you have to complain about is the color of the "table" in the simulation, then I can live with that. :) For what it's worth I was trying to mimic the color of the table used in the video so that they would look similar when side by side!

[@coreC..]

I did not make the connection with the table. Funny.. I thought of a ground plane, sand and dirt. Btw. I am totally zen with the color too. Brown is just one of the hardest colors, for me, while mixing colors for an oil-painting. It's just me.. Your content is what it is all about, and You, like others notice as well, have a quality for teaching. Your personality, your knowledge about science, how you presentate, obviously well prepared but it all still feels comfortable absorbing the info. David.subscribers++; // no comment

[@VeteranVandal]

I learned you are pretty good at pool... Or the highlights are. Also... Was that porcelain?

[@AllThingsPhysicsYouTube]

I can definitely pull off some good shots, but I don't practice enough to be considered good; I'm not very consistent. I learned a few things from my brothers last summer and it got me thinking about making such a video.

[@VeteranVandal]

@@AllThingsPhysicsKZbin idk but that backspin was very good.

[@morchel332]

frickin freaky friction

[@Miss_Trillium]

69 tries? Nice

[@AllThingsPhysicsYouTube]

Believe it or not, totally random.

[@jorgeparreira3037]

69 is nice and all, but like thats a lot of times to throw a disc man, props

[@AllThingsPhysicsYouTube]

Don't I know it! But once I decided that would be a cool thing to end with I just had to keep going until I got it.

[@Encysted]

nice

[@AllThingsPhysicsYouTube]

Thanks

[@SquashyPan]

I am a phd in physics and I want to say nice video! but I also want to point out that it took 69 attempt to stop the wheel so.....nice video!

[@AllThingsPhysicsYouTube]

Yes, it was surprisingly difficult to throw the wheel with just the right amount of backspin. And believe it or not, the fact that it took 69 attempts was completely random.

[@1jay288]

Вопрос не потеме!, задавал его многим, кто освещает физику на ютуб, но так ни кто и не ответил " условия задачи: имеем ампер-весы, теперь берем ампер-Рычаг!!!! Вопрос:" какой будет баланс мощности, если на концах ампер-рычага будут находится устроиства использующие индукцию Фарадея??? "🤔🤔🤔

[@morchel332]

int10-13 2xdx attempts

[@morchel332]

dont be a d³x/dt³ :

[@AllThingsPhysicsYouTube]

Cute...

[@AllThingsPhysicsYouTube]

Cute again...

[@adb012]

It HAD to be 69, right?

[@AllThingsPhysicsYouTube]

Heh. Believe it or not that was a total coincidence. It really did turn out to be 69 tries.

[@adb012]

@@AllThingsPhysicsKZbin ... If you say it, I believe it.

[@BariumCobaltNitrog3n]

But...why would you want the cue ball to do that? That's ball-in-hand for your opponent. You need that collision to get a ball in.

[@AllThingsPhysicsYouTube]

You use it to put the cue ball in a good location to make your next shot easier. It is assumed you will make this shot.

[@kutbuddinrangwala1039]

69

[@AllThingsPhysicsYouTube]

Believe it or not, that was random!

[@kutbuddinrangwala1039]

@@AllThingsPhysicsKZbin 😆

[@ryanconners3048]

Nice

[@AllThingsPhysicsYouTube]

Thanks!